Vinyl polymers, such as polyvinyl chloride, polyvinyl acetate, polystyrene, and the like, excel in physical and chemical properties, are easy to mold, and are widely used as general purpose resins. However, the recent expansion of their range of use has made it difficult to use vinyl polymers in many potential applications because of their inherent limiting physical properties. Some of these properties, such as electrical characteristics, water resistance, and the like, have to be modified to meet the needs and requirements of various applications.
Liquid phase polymerization procedures, such as emulsion polymerization, solution polymerization and sometimes suspension polymerization, are used to prepare vinyl polymers.
In emulsion polymerization, the monomers are dispersed as small droplets in a water solution of an emulsifier by agitation. After addition of catalyst (or initiator), polymerization occurs in emulsifier micelles (small association clusters) forming latex particles to which the monomers migrate from the droplet reservoirs. The temperature is controlled by the transfer of heat from or to the water medium surrounding the latex particles. Product polymer particles can be separated by filtration or centrifugation.
In solution polymerization, water is vigorously excluded to assure efficient use of the catalyst. The catalysts are different from those used in emulsion polymerization processes. The monomers are diluted with an organic solvent and polymerized in solution by the addition of the catalyst. The organic solvent serves as the reaction medium as well as a heat transfer medium. Bulk polymerization is a special form of solution polymerization but is seldom used for vinyl polymer manufacture. Product polymer is recovered from the residual solvent phase.
Suspension polymerization is similar in some respects to emulsion polymerization and is used to make some vinyl polymers. In suspension polymerization, liquid monomer is dispersed in water in the form of tiny droplets in a stirred reaction vessel. Usually, a polymerization initiator, such as a peroxide, is dissolved in the monomer phase. Upon heating, polymerization takes place in the monomer droplets in a manner essentially identical with mass polymerization. The continuous, low viscosity water phase facilitates heat transfer through the jacket of the reaction vessel. The product polymers are a dispersion of small polymer particles which can be separated from the water phase by filtering or centrifugation.
One technique for modifying vinyl polymer properties is to incorporate a reactive modifier into the product polymer structure during polymerization. However, known reactive modifiers are generally either unsatisfactory or have little useful modifying effect particularly in modified vinyl polymers made by solution polymerization.
The vinyl polymer art needs a new and improved solution polymerization procedure employing a new and effective reactive modifier in order to produce new and very useful modified vinyl polymer products with improved physical properties.